1. Maintaining dynamic equilibrium in living systems.
Homeostasis:
Maintaining dynamic equilibrium in living systems.
[or keeping us alive]

2. So…what does it all mean?
To keep the balance, an organism must
sense changes in external and internal environment
respond to those changes
Examples:
Cells in your brain are sensitive to changes (even small) in the levels
of oxygen and sugar.
low blood sugar triggers the liver to release stored sugar
when you stand up quickly, blood pressure increases to keep
oxygen flow to your brain.
Homeostasis is a characteristic of all living things.

3. Homeostasis
The body’s ability to maintain a relatively constant state.
Temperature
Water Balance
Glucose Levels
Oxygen & Carbon Dioxide Levels
And many, many more…

4. Temperature Cold Sense: Neurons in our skin Response:
change in blood flow
increased heart rate
constriction of blood vessels close to the surface
keeps brain, liver, and heart constant (core)
(37˚C)
shivering

5. Temperature Hot Sense: Neurons in our skin Response:
change in blood flow
dilation of blood vessels close to the surface
diverts blood flow away from internal organs
sweating

6. Homeostasis & Water Balance
The Urinary System:
Disposing of Wastes

7. Waste Products
The body produces many waste materials each day.
Wastes become toxic if they build up
Wastes and how they are disposed include:

8. The Urinary System
Rids the body of urea
Liver converts ammonia into urea
Kidneys are the main organ
Eliminate urea from the body (secretes)
Adjusts fluid volumes and regulates blood pressure (restores and reabsorbs)
Filters
125 mL of water
is filtered each
minute = 180 liters
per day!

9. Or why we breath hard during exercise!
CO2 and the Effect On pH
Or why we breath hard during exercise!

10. As we exercise breathing and heart rate increase.
CO2 builds up in blood because of muscles burning nutrients to make energy.
Increased CO2 causes the blood to become more acidic.
The human body doesn’t tolerate changes in pH.

11. Special receptors in nerve cells in the aorta, brain, and arteries that lead to the head monitor the pH.
When the pH begins to drift out of normal range ( ), these receptors are engaged.
This causes the brain to send signals to begin breathing at a faster rate.
By breathing faster, more CO2 is exhaled bringing the pH back to normal.

12. If too much CO2 is exhaled, like when one hyperventilates, the pH begins to drift the other way and becomes more alkaline.
If this happens, the receptors register a lack of O2.
The person will faint and the brain will slow breathing down to balance the amount of O2 in the body.
One way to fix this is to have person inhale and exhale into a paper bag. The CO2 balance is regained and the breathing slows down.

13. So….what happens when something
goes wrong?

14. What Works Together? To keep the balance!
The hypothalamus: part of the nervous system
Regulates water balance, body temperature, feeding,
sleep, and works with the endocrine system.
The endocrine system: release chemical
Messengers into the blood (hormones).
The nervous system, respiratory system,
urinary system, circulatory system, digestive system, and so on…
To keep the balance!

15. Feedback
In response to a condition, the body responds by adjusting internal conditions.
Negative feedback: changes that correct an abnormal situation
i.e. dehydration (goes away from a situation)
Positive feedback: critical process must completed quickly.
I.e. blood clot. (goes toward a situation)